7.3Redox

Redox

Oxidation Is Loss of electrons or the gain of oxygen, Reduction Is Gain of electrons or loss of oxygen. Remember OIL RIG.

Redox reaction is a reaction where reduction and oxidation happen, where there is electron transfer. Reduction and oxidation must happen together. One substance gives electron(s) to the other. In a redox reaction the substances will change oxidation state (their charge will change). Oxidation state is written using roman numerals when there is a transition metal in a word equation. Reducing agents are oxidised and oxidising agents are reduced. Oxidation state is written like this Iron(III)  = Fe3+

(a reaction where different atoms of the same element are reduced and oxidised is a disproportionation reaction) Examples to know (page 111):

-potassium iodide will go from colourless to red-brown, it is a reducing agent, it therefore is oxidised to produce I2 H2O2 + 2KI + H2SO4→ I2 + K2SO4 + 2H2O

2I- (colourless) → I2 (red-brown)

-Potassium mangenate, an oxidising agent, will go from purple to colourless. (Recall of equations involving KMnO4 is

not required.)

-potassium dichromate, an oxidising agent: Cr2O72- (orange) → 2Cr3+ (green)